Milling, like turning, is a way of "machining with a geometrically defined cutting edge". Unlike turning, however, the tool rotates during milling - not the workpiece.
In this production method primarily flat surfaces are produced. The associated method is called "face milling". On the other hand, "round milling" produces circular cylindrical surfaces.
In "screw" and "hobbing" helical screw surfaces or gears are produced.